RENAL,ENDOCRINE AND VASCULAR EFFECTS OF ATRIAL-NATRIURETIC-PEPTIDE INA NOVEL VASOPRESSIN-DEFICIENT GENETICALLY HYPERTENSIVE STRAIN OF RAT

In the absence of the potentially confounding influence of vasopressin in hypertension, the effects of atrial natriuretic peptide (ANP) on a rterial blood pressure and renal handling of water and sodium were ass essed from comparison of responses to intravenous ANP infusion in anae sthetized vasopressin-deficient New Zealand genetically hypertensive ( DI/H) rats and their normotensive substrain (DI/N). After 320 min of h ypotonic saline infusion, plasma ANP concentration was significantly h igher in DI/H compared with DI/N rats. ANP administration increased ci rculating ANP concentration in both groups. Plasma angiotensin II conc entration was higher in DI/H than in DI/N rats; infusion of ANP raised circulating angiotensin II in both groups though this achieved statis tical significance only in DI/N rats. Plasma aldosterone concentration s were initially similar in normotensive and hypertensive animals and, in both, were reduced markedly by i.v. ANP infusion. Administration o f ANP produced sustained hypotension in both groups. However, the hypo tensive effect of ANP was more pronounced in DI/H compared with DI/N r ats. Heart rate was initially similar in the two groups, and infusion of ANP produced no detectable change. By comparison with animals maint ained on hormone-free infusate, urine flow increased markedly over the 80 min period of ANP infusion in both groups, by 142 % in DI/H rats a nd 127 % in DI/N rats. ANP administration produced a natriuresis in bo th groups but the increase in Na+ excretion was much greater in DI/H ( 342 %) than in DI/N (139 %) rats. It appears from the current study th at vasopressin-deficient hypertensive rats are more sensitive to ANP w ith regard to effects on blood pressure and renal excretion than their vasopressin-deficient normotensive substrain. These differences may, in part, reflect adjustments to long-term elevation in blood pressure and in plasma ANP concentration in hypertension and, in part, rely on the associated disturbances in related endocrine systems.